Reflectivity studies

Monolayers can be transferred onto many different substrates. Most LB depositions have been perfonned onto hydrophilic substrates, where monolayers are transferred when pulling tire substrate out from tire subphase. Transparent hydrophilic substrates such as glass [18,19] or quartz [20] allow spectra to be recorded in transmission mode. Examples of otlier hydrophilic substrates are aluminium [21, 22, 23 and 24], cliromium [9, 25] or tin [26], all in their oxidized state. The substrate most often used today is silicon wafer. Gold does not establish an oxide layer and is tlierefore used chiefly for reflection studies. Also used are silver [27], gallium arsenide [27, 28] or cadmium telluride wafer [28] following special treatment. 

Wang J, Ocko B M, Davenport A J and Isaacs H I 1992 In situ diffraction and reflectivity studies of the Au(111 )/electrolyte interface Reconstruction and anion adsorption Phys. Rev B 34 10 321-38... 

Adzic R R, Yeager E and Cahan B D 1977 Specular reflectance studies of bromine adsorption on gold J. Electroanal. Chem. 85 267-76... 

The measurements of concentration gradients at surfaces or in multilayer specimens by neutron reflectivity requires contrast in the reflectivity fiDr the neutrons. Under most circumstances this means that one of the components must be labeled. Normally this is done is by isotopic substitution of protons with deuterons. This means that reflectivity studies are usually performed on model systems that are designed to behave identically to systems of more practical interest. In a few cases, however (for organic compounds containing fluorine, for example) sufficient contrast is present without labeling. 

You H, Zurawski DJ, Nagy Z, Yonco RM. 1994. In-situ X-ray reflectivity study of incipient oxidation of Pt(lll) surface in electrolyte-solutions. J Chem Phys 100 4699-4702. 

Li ZX, Dong CC, and Thomas RK. 1999. Neutron reflectivity studies of the surface excess of Gemini surfactants at the air-water interface. Langmuir 15(13) 4392 -396. 

Salts of the hexafluoroosmate(IV) anion, OsFi-, are readily obtained by the hydrolysis of the corresponding hexafluoroosmate(V) species (q.v.) (47, 48), and for K2OSF6 a magnetic moment of 1.48 B. M. at 300 °K has been reported (49), which is in accordance with the expectation of a low-spin 3Tlg (t g) ground state. Some early spectroscopic measurements were made for OsF in aqueous solution by Hepworth et al. (48), who reported a weak band at 32.5 kK. and a much stronger one just above 50 kK., but more recently diffuse reflectance studies have been reported by Brown et al. (32) and by Allen et al. (11). 

Probably the first instrument designed for reflectance studies was that described by Nutting [8], and improved by Taylor [9]. Since that time, a large number of instruments have been proposed, and numerous modifications suggested to continually improve signal-to-noise ratios [1,2]. 

The utilization of IR spectroscopy is very important in the characterization of pseudopolymorphic systems, especially hydrates. It has been used to study the pseudopolymorphic systems SQ-33600 [36], mefloquine hydrochloride [37], ranitidine HC1 [38], carbovir [39], and paroxetine hydrochloride [40]. In the case of SQ-33600 [36], humidity-dependent changes in the crystal properties of the disodium salt of this new HMG-CoA reductase inhibitor were characterized by a combination of physical analytical techniques. Three crystalline solid hydrates were identified, each having a definite stability over a range of humidity. Diffuse reflectance IR spectra were acquired on SQ-33600 material exposed to different relative humidity (RH) conditions. A sharp absorption band at 3640 cm-1 was indicative of the OH stretching mode associated with either strongly bound or crystalline water (Fig. 5A). The sharpness of the band is evidence of a bound species even at the lowest levels of moisture content. The bound nature of this water contained in low-moisture samples was confirmed by variable-temperature (VT) diffuse reflectance studies. As shown in Fig. 5B, the 3640 cm-1 peak progressively decreased in intensity upon thermal... 

P. Salvador, Potential distribution and photovoltage origin in nanostructured Ti02 sensitization solar cells an interference reflection study, J. Phys. Chem. B 105 (2001) 9732-9738. 

A. Rakai, D. Tessier, and F. Bozon-Verduraz, Palladium-alumina catalysts A diffuse reflectance study, New J. Chem. 16, 869-875 (1992). 

C. Stubenrauch, P.A. Albouy, R. Kitzling, and D. Langevin Polymer/Surfactant Complexes at the Water/Air Interface A Surface Tension and X-Ray Reflectivity Study. Langmuir 16, 3206 (2000). 

The thinnest liquid film consist mainly of the bilayer of surface-active substance (such as soap = 50 A) and some layers of water. The light interference and reflection studies show many aspects of these TLFs. 

Larramona, G. Gutierrez, C. (1989) The passive film on iron at pH 1-14. A potential-modulated reflectance study. J. Electrochem. 

Malengreau, N. Muller, J.P. Calas, G. (1994) Fe-speciation in kaolins A diffuse reflectance study. Clays Clay Min. 42 137-147... 

Iron oxides in laterites a combined mineralogical, magnetic, and diffuse reflectance study. Schweiz. Mineral. Petrogr. Mitt. 

Poling, G.W. (1969) Infrared reflection studies of the oxidation of copper and iron. J. Electro-chem. Soc. 116 958... 

X-ray reflectivity studies and II-A isotherms revealed a similar model in which the dendrons project the hydrophUic crowns into the water phase and the hydrophobic chains perpendicular to the interface. Amphiphihc dendronized polymers that adopt a cylindrical, rodlike morphology, projecting hydrophihc and hydrophobic dendrons on opposite faces of the stmcture, form stable monolayers exhibiting collapse pressures of approximately 20mN/m (Fig. 11.41). 

Pao W-J, Stetzer MR, Heiney PA, Cho W-D, Percec V. X-ray reflectivity study of Langmuir films of amphiphilic monodendrons. J Phys Chem B 2001 105 2170-2176. 

Dickinson, E., Horne, D.S., Phipps, J.S., Richardson, R.M. (1993a). A neutron reflectivity study of the adsorption of p-casein at fluid interfaces. Langmuir, 9, 242-248. 

When light is directed onto a sample it may either be transmitted or reflected. Hence, one can obtain the spectra by either transmission or reflection. Since some of the light is absorbed and the remainder is reflected, study of the diffuse reflected light can be used to measure the amount absorbed. However, the low efficiency of this diffuse reflectance process makes it extremely difficult to measure 120) and it was speculated that infrared diffuse reflection measurements would be futile 120). Initially, an integrating sphere was used to capture all of the reflected light121) but more recently improved diffuse reflectance cells have been designed which allow the measurement of diffuse reflectance spectra using FT-IR instrumentation 122). 

Paik, C. S., Hu, C. B. Surface Chemical Analysis of Segmented Polyurethanes. Fourier Transform IR Internal Reflection Studies in Advances in Chemistry Series,Cooper, S., Estes, G. (Eds) 176, 69 (1979)... 

A preliminary examination of coal materials associated with igneous intrusions from two general areas in Colorado has been completed. A study of the field relationships, petrographic examination, chemical analyses, and reflectance studies has been conducted. Results can be summarized as follows ... 

Based on steady-state and time-resolved emission studies, Scaiano and coworkers have concluded that silicalite (a pentasil zeolite) provides at least two types of sites for guest molecules [234-236], The triplet states of several arylalkyl ketones and diaryl ketones (benzophenone, xanthone, and benzil) have been used as probes. Phosphorescence from each molecule included in silicalite was observed. With the help of time-resolved diffuse reflectance spectroscopy, it has been possible to show that these triplet decays follow complex kinetics and extend over long periods of time. Experiments with benzophenone and arylalkyl ketones demonstrate that some sites are more easily accessed by the small quencher molecule oxygen. Also, diffuse reflectance studies in Na + -X showed that diphenylmethyl radicals in various sites decay over time periods differing by seven orders of magnitude (t varies between 20/is and 30 min) [237]. 

Neutron and X-ray reflectivity studies of adsorbed block copolymers... 

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